Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
Once the ink is melted, it typically drips into an ink reservoir. The reservoir is coupled by conduits to a print head for jetting the liquid ink onto the recording medium. In color printers, a print head is provided for each composite color. For example, a color printer may have one print head for emitting black ink, another print head for emitting yellow ink, another print head for emitting cyan ink, and another print head for emitting magenta ink. Color images may be comprised of four images, one for each of the composite colors. The image data for each of the composite colors are provided to a print head controller for generation of a color image.
The print head controller uses the image data for a composite color to control the operation of the print head for the corresponding composite color. In some ink printers, the ink may be emitted by a print head directly onto a sheet of recording medium. In other printers called offset printers, the ink is emitted onto an intermediate revolving imaging drum. When an intermediate imaging drum is used, several revolutions of the imaging drum may occur before the complete image is generated. Once the image is generated, a transfer roller engages the imaging drum and a sheet of recording medium is fed into the nip between the imaging drum and the transfer roller. The pressure and heat in the nip transfer the inked image from the imaging drum onto the recording medium. The sheet bearing the image, in both direct and offset printing, is then transported to a discharge area.
The print head in an ink printer may be comprised of many piezoelectric ejectors that expel a small amount of ink when energized by a voltage signal. The ejectors are arranged in a print head in a row and column matrix. The voltage signals for the ejectors are selectively generated by the print head controller in correspondence with the pixilated image data. Thus, the print head controller causes the ejectors of the print head to emit droplets of ink that are deposited on a media sheet or an imaging drum as it passes the print head to form an image.
Recording media sheets, particularly paper, can produce fibers and other particulate matter as they move from the supply stack through the transfer nip to the discharge area. These particulates and fibers along with dust typically present in air may enter the gap between a print head and an imaging drum. Some of the fibers and particulate may clog nozzles of the ejectors in a print head. The risk of paper fibers and particulates clogging print head nozzles is especially present in direct printing machines because the media sheet is brought so close to the print head for printing. Clogged nozzles adversely impact the quality of the images generated by the printing machine.